The present invention relates to a fluorescent lamp capable of adjusting a mercury vapor pressure in a discharge tube by using an amalgam.
A fluorescent lamp uses fluorescence, which is obtained by exciting a fluorescent substance layer formed on an inner wall of a glass tube with an ultraviolet ray, as a light source. As the ultraviolet ray, a resonance line of mercury is widely used. In general, pure mercury is filled in a glass tube of a fluorescent lamp. In such a fluorescent lamp, when the temperature of the coolest portion of the lamp is about 40xc2x0 C. and the ambient temperature around the lamp is about 25xc2x0 C., the mercury vapor pressure in the glass tube becomes suitable, and the maximum luminous efficiency can be attained. However, in a compact fluorescent lamp produced, for example, by using a bent glass tube such as a U-shaped glass tube, etc. or, by connecting a plurality of glass tubes, the ambient temperature around the lamp is easily increased. Consequently, the lamp temperature tends to be increased.
Therefore, there have been proposed methods for placing a mercury amalgam pellet at a portion corresponding to the coolest portion in a fluorescent lamp so that the mercury vapor pressure in the glass tube is adjusted to fall within the appropriate range even if the temperature of the fluorescent lamp is increased. The mercury amalgam pellet is generally placed in the slender glass tube that is provided so as to be in communication with the glass tube that is a discharge tube. In this case, a slender glass tube is provided with a means for adjusting the location of the amalgam pellet and for preventing the mercury amalgam pellet from moving toward the inside of the discharge tube. Examples of the structure of the fluorescent lamp having such a means include, for example, a structure shown in FIG. 7 (disclosed in, for example, JP 2-16513 Y), a structure including a member for preventing the mercury amalgam pellet from moving toward the inside of the glass tube (which will also be referred to as xe2x80x9ca moving prevention memberxe2x80x9d hereinafter) in a slender glass tube, or the like. The structure of the fluorescent lamp shown in FIG. 7 includes a glass tube 10 having a fluorescent substance layer 11 on the inner surface, a sealed portion 12 provided at the end of the glass tube 10, and a slender glass tube 14 penetrating through the sealed portion 12, and the slender glass tube 14 has a narrow portion 15 on the portion protruding outward from the sealed portion 12. In the fluorescent lamp shown in FIG. 7, between the end of the slender glass tube 14 and the narrow portion 15, a mercury amalgam pellet 13 is held.
Recently, in a compact fluorescent lamp such as a compact self-ballasted fluorescent lamp, as further miniaturization increasingly has been demanded, a more slender glass tube has been used as a discharge tube. As to a slender glass tube containing a mercury amalgam pellet, a further slender and shorter tube tends to be used. When such a slender and short slender glass tube is used, in a structure shown in FIG. 7, the part of the slender glass tube 14 protruding outward from the sealed portion 12 is shortened. Therefore, it is difficult to form a narrow portion 15 while securing a sufficient portion containing mercury amalgam pellet 13. Furthermore, there is a risk that a slender glass tube 14 may be pressed and collapsed when the narrow portion 15 is formed. Furthermore, in the structure in which the moving prevention member is inserted into the slender glass tube, when the slender glass tube is used as an evacuation tube in manufacturing the fluorescent lamp, the moving prevention member may inhibit a smooth evacuation, which may lead to a defective evacuation in the fluorescent lamp.
It is an object of the present invention to solve the problems of the prior art. That is, the object of the present invention is to provide a fluorescent lamp capable of reliably preventing a mercury amalgam pellet from moving toward the inside of a glass tube while fully securing a portion for containing the mercury amalgam pellet.
In order to achieve the above-mentioned objects, according to a first aspect of the present invention, a fluorescent lamp includes a glass tube having a fluorescent substance layer on the inner surface, a sealed portion formed at the end of the glass tube, a container having an inner space that is in communication with the inside of the glass tube and is not in communication with the outside of the glass tube, and a mercury amalgam pellet contained in the container. In the fluorescent lamp of this configuration, the sealed portion is provided with a through hole for allowing communication between the glass tube and the container, and at least a part of the through hole in the sealed portion has an inner diameter smaller than the diameter of the mercury amalgam pellet.
With the fluorescent lamp having such a configuration, since the portion for preventing the moving of the mercury amalgam pellet is formed in the sealed portion, it is possible to prevent the moving of the mercury amalgam pellet while fully securing the volume of the container, regardless of the length of the portion of the container protruding outward from the sealed portion. Furthermore, since there is no member corresponding to the moving prevention member in the through hole and the container, it is possible to attain sufficient evacuation efficiency even when the container and the through hole are used as an evacuation tube.
It is preferable in the above-mentioned fluorescent lamp that at least a part of the container is placed in the sealed portion. According to such a preferred configuration, even when the length of a portion of the container protruding outward from the sealed portion is short, it is possible to fully secure the sufficient volume of the container.
According to another aspect of the present invention, a fluorescent lamp includes a glass tube having a fluorescent substance layer on the inner surface, a sealed portion formed at the end of the glass tube, a slender glass tube having an inner space that is in communication with the inside of the glass tube and is not in communication with the outside of the glass tube, and a mercury amalgam pellet contained in the slender glass tube. In the fluorescent lamp of this embodiment, the slender glass tube having a small-diameter part with an inner diameter smaller than the diameter of the mercury amalgam pellet and a large-diameter part with an inner diameter larger than the diameter of the mercury amalgam pellet, is welded to the glass tube so that the small-diameter part is placed in the sealed portion and the large-diameter part is placed further away from the glass tube than the smaller-diameter part.
Also in the fluorescent lamp having such a configuration, since the portion for preventing the moving of the mercury amalgam pellet is formed in the sealed portion, it is possible to prevent the amalgam pellet from moving while fully securing the volume of the portion for containing the mercury amalgam pellet. Furthermore, since there is no member corresponding to the moving prevention member in the slender glass tube, even when the glass tube is used as an evacuation tube, it is possible to attain sufficient evacuation efficiency.
It is preferable in the above-mentioned fluorescent lamp that at least a part of the large-diameter part is placed in the sealed portion. With such a preferred configuration, even in a case where the part of the slender glass tube protruding outward from the sealed portion is short, it is easy to secure the sufficient volume of the portion containing the mercury amalgam pellet.
According to a further aspect of the present invention, a method for manufacturing a fluorescent lamp includes: inserting a molding stick having a large-diameter part and a small-diameter part, which have different diameters, into a slender glass tube; forming a fluorescent substance layer on the inner surface of a glass tube; placing the slender glass tube at the open end of the glass tube so that the large-diameter part of the molding stick is located further away from the glass tube than the small-diameter part of the molding stick; sealing the open end of the glass tube and then drawing out the molding stick from the slender glass tube; placing a mercury amalgam pellet in the slender glass tube; and sealing an open end of the slender glass tube located outward from the glass tube. In such a method, when sealing the open end of the glass tube, at least a part of the slender glass tube in which the small-diameter part of the molding stick is inserted is welded to the glass tube, and the inner diameter of the slender glass tube is kept larger than the diameter of the amalgam pellet in the part in which the large-diameter part of the molding stick is inserted and is reduced to be smaller than the diameter of the mercury amalgam pellet in the part in which the small-diameter part of the molding stick is inserted and welded to the glass tube.
The phrase xe2x80x9chaving a large-diameter part and a small-diameter part, which have different diametersxe2x80x9d means that the molding stick has two parts each having a different diameter and the part having a larger diameter is referred to as a large-diameter part and the part having a smaller diameter is referred to as a small-diameter part.
According to such a manufacturing method, a portion for preventing the moving of the mercury amalgam pellet can be formed while the glass tube is sealed at the same time, and, in addition, can be formed in the sealed portion. Furthermore, even after the sealing process, the slender glass tube has a larger diameter than that of the mercury amalgam pellet in the part in which the large-diameter part of the molding stick is inserted. Consequently, it is easy to secure the portion for containing the mercury amalgam pellet. Therefore, it is made possible to manufacture the fluorescent lamp of the present invention without separately carrying out a process for molding the slender glass tube. Furthermore, when reducing the inner diameter of a certain part of the slender glass tube, the molding stick is inserted into the slender glass tube, so that it is possible to prevent the slender glass tube from being pressed and collapsed. Therefore, even when the slender glass tube is used as an evacuation tube, it is possible to attain sufficient evacuation efficiency.
It is preferable in the above-mentioned method that the glass tube is evacuated by using the slender glass tube as an evacuation tube before placing the mercury amalgam pellet in the slender glass tube. When a member other than the slender glass tube is used as an evacuation tube, after the mercury amalgam pellet is inserted into the slender glass tube and before the evacuation is completed, it is necessary to cool the glass tube and slender glass tube in order to prevent the releasing of mercury from the mercury amalgam pellet. However, according to such a preferred embodiment of the present invention, the above-mentioned cooling operation is not necessary because the mercury amalgam pellet is inserted into the glass tube after evacuation.